This invention relates to improvements in a thin-film optical switching device.
In order to put systems for processing and communicating optical information by the use of laser light to practical use, the optical circuit elements should be combined into an integrated circuit. If mechanical means for rotating a mirror or a prism is unavailable, it is possible to modulate or deflect an optical wave by changing the refractive index of the particular medium through which the optical wave travels. This measure can be achieved by utilizing the electro-optical effect, magneto-optical effect or acousto-optical effect according to which the substance involved changes in refractive index. For example, there have been already proposed thin-film optical switching and modulating devices utilizing such effects.
Among them thin-film optical switching devices utilizing the acousto-optical effect are promising because they can employ a substrate of noncrystalline material, for example, glass, as long as the substrate is operatively associated with a suitable transducer for generating an elastic surface wave and because there is no necessity for using a thin film composed of a special electro-optical or magneto-optical crystal for the wave guide and the substrate. Among optical switching devices utilizing an elestic surface wave there are well known (a) optical switching devices including a quartz substrate and a thin-film optical waveguide formed by sputtering Corning glass No. 7059 upon the substrate, (b) those including a substrate of ferroelectric lithium niobate (LiNbO.sub.3) and a thin-film optical waveguide formed by sputtering chalcognide glass on the substrate or by diffusing a suitable metal or its oxide into the surface layer of the substrate, (c) those including a substrate made of fused quartz or glass available under the trade mark PYREX and an electro-mechanical transducer with interdigital electrodes and an optical waveguide each formed of a thin film of zinc oxide (ZnO) disposed on the substrate.
The devices (a) have had low light deflection or diffraction efficiency, and the devices (b) have had a high optical propagation loss while they have not been suitable for efficiently coupling to other optical circuit elements not requiring a substrate of ferroelectric crystals. Also the devices (c) have had a high optical propagation loss and a low light diffraction efficiency. Thus all the devices as above described have been disadvantageous in that it is difficult to simultaneously have low propagation and coupling loss and high diffraction efficiencies. In other words, such devices have not been practically available far integrated optical circuits.
Accordingly it is a general object of the present invention to eliminate the disadvantages of optical switching elements of the conventional types as above described.
It is an object of the present invention to provide a new and improved thin-film optical switching device having a low light propagation loss and high light diffraction efficiency yet which is still easy to couple to and integrate with other thin-film optical circuit elements.